1. Field of the Invention
The invention relates to a rebound-type hardness tester and, more specifically, to an Equotip type hardness tester in which an indenter hammer is caused to impact against a specimen and the hardness of the specimen is measured from the ratio between the velocities of the indenter hammer before and after the impaction.
2. Description of the Related Art
A rebound type hardness tester, in which an indenter hammer is caused to impact a specimen and the hardness of the specimen is calculated from the ratio between the velocity of the indenter hammer immediately before the impaction (impacting velocity) and the velocity of the same immediately after the impaction (rebounding velocity), is generally called an Equotip type hardness tester and put to practical use.
Since the indenter hammer in the Equotip type hardness tester is adapted to be shot by means of a coil spring, it is not necessarily required, in hardness measurement, that the Equotip type hardness tester is set in the position to keep the impacting direction straight down. Namely, it is possible to carry out the hardness measurement with the Equotip type-hardness tester (the body 1 formed of a cylindrical handle portion 11 and a measuring cylinder 12 connected to it) tilted, i.e., keeping the impacting direction, for example, in the horizontal direction, in an angle of depression of 45xc2x0, in an angle of elevation of 45xc2x0, and in the direction straight up (the angle of inclination then formed between the body 1 and the horizontal plane 010 is denoted by 0) and with the front end of the measuring cylinder 12 abutting on the specimen 01 as shown in FIG. 3. Thus, such an advantage is obtained that hardness of the side face of bottom face of a specimen can be freely measured.
The indenter hammer 3 is adapted to be discharged in the axial direction of the body 1 guided by the cylindrical body 1. Further, there are provided a permanent magnet within the indenter hammer 3 and a velocity detecting coil 4 wound around the front end portion of the measuring cylinder 12, and, by the movements of the permanent magnet (i.e., the indenter hammer 3), electric currents proportional to the impacting velocity and the rebounding velocity are causes to flow through the velocity detecting coil 4. The currents are converted into voltages by a voltage transformer 5 within a display unit 6, the voltages are input to a CPU 7 to calculate the hardness, and the calculated value is displayed as the Equotip hardness L of the specimen on a display 8. The Equotip hardness L is defined by a later described expression (1).
The velocity impacting the specimen 01 of the indenter hammer 3 when hardness is measured with the body 1 tilted is different from its velocity produced when the body 1 is held in the upright position. Therefore, it has so far been practiced to obtain the correct hardness value by checking the value (hardness) of the result obtained by the tilted measurement with a table (conversion table) for angular correction. There is such a one put to practical use that automatically performs the angular correction by means of an incorporated CPU. Further, there is also used a one put to practical use that automatically converts an obtained hardness value into a standardized hardness value so far in use (e.g., Brinell, Vickers, Rockwell, C, and Shore hardness) and displays the hardness value.
The principle of measurement in the Equotip type hardness tester will be described with reference to FIG. 4. Referring to FIG. 4, reference numeral 3 denotes an indenter hammer and 01 denotes a specimen. The indenter hammer 3 is shot by a coil spring (not shown) incorporated in the measuring cylinder 12 to impact the specimen and then rebound from the same.
At this time, if friction and air resistance against the indenter hammer 3 in motion is neglected and it is assumed that no external force other than the gravitational force acts on the indenter hammer 3 after it has been discharged, the hardness L of the specimen 01 is defined by the following expression
L=(|V2|/|V1|)xc3x971000 xe2x80x83xe2x80x83(1) 
where
V1: impacting velocity of the indenter hammer,
V2: rebounding velocity of the indenter hammer.
In the conventional Equotip type hardness tester, detection of the velocities of the indenter hammer 3 (the impacting velocity against and rebounding velocity from the specimen 01) is performed by measuring voltages produced in the coil at the time when the permanent magnet incorporated in the indenter hammer 3 passes by the velocity detecting coil.
Generally speaking, the voltage change occurring in the velocity detecting coil (in pulse waveform) varies with the velocity at which the permanent magnet passes by the coil. Namely, the slower the passing velocity of the permanent magnet, the duller becomes the pulse waveform W (as shown by dotted lines in FIG. 5). From this, a problem arises that accurate measurement results cannot be obtained.
Further, there is also such a problem that when the specimen is a magnetic body or it is magnetized or the environment is magnetized, an accurate result of measurement cannot be obtained due to the effect of such magnetism.
It is an object of the invention to provide a method of detecting velocities of the indenter hammer in an Equotip type hardness tester whereby the above mentioned problems are solved and an Equotip type hardness tester in which the aforesaid detecting method is carried out.
As the means for solving the above problems, a method according to the invention of detecting velocities of an indenter hammer in an Equotip type hardness tester, including a measuring cylinder constituting the body of the hardness tester and providing a passage for the indenter hammer to go forward and backward, the measuring cylinder having two light receiving holes formed therein a distance S apart in the axial direction thereof, comprises the steps of measuring the times required for the indenter hammer to go forward and backward past the two light receiving holes and detecting the velocities of the indenter hammer in accordance with the required times and the distance S.
As the means for solving the above problems, the required times are calculated by having a pulse counter, to which time pulses generated by a pulse generator are input, count the number of the timing pulses from the moment of receipt of a signal indicating that the indenter hammer passed by one light receiving hole of the two light receiving holes to the moment of receipt of a signal indicating that the same passed by the other light receiving hole.
As the means for solving the above problems, an Equotip type hardness tester according to invention comprises a measuring cylinder constituting the body of the hardness tester and providing a passage for an indenter hammer to go forward and backward, a coil spring incorporated in the body, an indenter hammer adapted to be shot by the spring force of the coil spring toward a specimen, a velocity sensor attached to the body for measuring the velocities of the indenter hammer immediately before impacting against the specimen and immediately after the impaction, and a display unit including a CPU receiving information of the velocities of the indenter hammer detected by the velocity sensor for calculating hardness of the specimen and a display for displaying thereon the hardness of the specimen calculated by the CPU, wherein the velocity sensor is constituted of two light projecting holes formed in the vicinity of the front end portion of the measuring cylinder a distance S apart from each other in the axial direction of the measuring cylinder and light receiving holes formed in the positions corresponding to the light projecting holes, and, further, light sources provided for each of the light projecting holes and photodetector devices provided for each of the light receiving holes.
In the invention, the indenter hammer, at the time of measurement, passes by the two light receiving holes formed a distance S apart in the axial direction of the measuring cylinder in the order of the inner light receiving hole and the outer light receiving hole in the impacting course, whereas it passes by them in the order of the outer light receiving hole and the inner light receiving hole in the rebounding course after impacting against a specimen.
Hence, by measuring the time required for the indenter hammer to pass by the light receiving holes in the impacting course and the time required for the same to pass by the light receiving holes in the rebounding course, the impacting velocity against and the rebounding velocity from the specimen (face) of the indenter hammer can be calculated in accordance with the measured times and the distance between the light receiving holes.
The aforesaid times can be calculated by using a pulse counter and by having numbers of timing pulses counted by the pulse counter.
Further, since the indenter hammer velocity (detecting) sensor is of a photoelectric type, it is made possible to carry out the detection having the detecting accuracy of the velocity of the indenter hammer unaffected by the indenter hammer velocity.
Further, the measurement can be carried out unaffected by magnetism.